In a previous question about soft lenses, it was suggested that much of the current practices regarding soft focus involve selectively soft focusing certain parts of the image and mattdm suggests its not as simple as a little blur.

What digital methods exists to give a selective approximate soft focus to photographs?

5 Answers
5

There are two separate parts to this; first, how to replicate the effect of a soft focus lens in software, and second, how to do what Jay notes in your other question is common practice in modern portrait photography: selective softening.

How to replicate soft focus due to spherical aberration

There are several techniques for this. First, here's a sample image (a photo of my daughter):

And here's that image with a simple gaussian blur.

Following the suggestion in the comment below, I've replaced the original examples with versions where I turned the sliders up a little higher than I had originally, so the effect is more apparent. It could be even more dramatic, but this is as un-timid as I could make myself go.

Apply a light gaussian blur to the top layer, and set it to be mostly transparent.

Adjust the curves middle layer to be quite bright. Apply a much wider gaussian blur to this layer. Set this to "Overlay" blend mode. (Soft Light would probably also work.) And, set the opacity to mostly (but not all) solid. The tutorial uses adjustment in Adobe Photoshop for this, which is a nice approach for experimentation.

The linked tutorial doesn't say this, but I found that it's nice to make a final adjustment to curves to get the overall brightness back in line.

I found this technique to be a bit tedious in Gimp, due to the lack of adjustment layers; you end up recreating and destroying the middle layer over and over again as you work to get the right effect. Anyway, a sample result:

Make a duplicate layer and apply a high-pass filter (as with sharpening, but with a moderately-high radius)

Invert that layer, and choose Overlay or Soft Light blend mode.

This is much simpler, and produces nice looking results with many images, although I think it's less technically similar to what a soft focus lens does. Result:

And finally, a third (and simple) technique based on Stan Rogers's answer. The steps here are based on Gimp; the actual details should be similar in Photoshop.

Create a duplicate layer.

Add a Layer Mask to that layer, based on a grayscale copy of the layer. Immediately apply the layer mask. This creates a layer where dark tones are more transparent but which is otherwise identical to the base layer. (There's probably a better way to do this... comments welcome.)

Apply a moderate gaussian blur to this layer. This creates the "ethereal halo" blur. Set the layer to Lighten Only blend mode, and adjust the layer opacity to taste. You can also leave it in the Normal blend mode for a different effect, or try Overlay or Soft Light.

Result:

Comparison

For comparison, I think it's handy to open each of these in its own tab and flip back and forth: origblur123. I think the last approach works best, but the others would have their uses in some images.

Selective Softening

For the second overall part to the question, I think usually a more simple approach is used, where one simply makes a blur layer and then erases the blur to varying degrees in areas where more sharpness is desired. (With no curves adjustment layer.) But that's not an area where I've done much work, since it doesn't fit with my own style and preferences.

I've tried it a little bit, and using one of the above approaches in combination with selective erasing can yield nicer final images than a simple blur layer. It's particularly important if you use the first technique, which can cause a lot of unwanted blur. If you have an image where you really want to post-process for this effect and have it look good, careful selective work is probably the thing to do.

If you don't mind me saying so, this is exactly why a soft-focus lens is The Better Way™ -- you're as timid with your effect as we all tend to be in post-processing. With a SF lens, you line the rig up, click a button and get a magical dreamy effect (assuming the lighting is decent). In post, you get the feeling that your softening your picture!!! -- and a mild to moderate panic reaction sets in. A plugin with a preset helps with the timidity (a little), but it's not the same. (+1, BTW)
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user2719Jun 19 '11 at 3:06

Thanks. I do not mind you saying so at all. Maybe I'll redo the examples with the sliders turned up a bit for more dramatic effect. I'd definitely rather have the SF lens.
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mattdmJun 19 '11 at 3:22

I've been doing zone plate and zone sieve work recently also, pretty cool stuff. I also tried pinhole (I'm using the skink system so it is easy to change) and that just seems to make it soft, not glowing...)
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Paul CezanneNov 16 '12 at 11:53

It would probably help to start with a definition of "soft focus". "Soft focus" is not just another way of saying "out of focus", at least not in the photographic vocabulary.

The classic soft focus lens is the Rodenstock Imagon. It was a lens that had a relatively large amount of spherical aberration, which means that the center of the lens doesn't focus at the same plane as its outside edges. Used without its signature "sink strainer" diaphragm, it was soft to the point that it was unusable. The diaphragms had a relatively large hole in the center, which, by itself, produced a relatively sharp picture -- not tack-sharp by today's standards by any means, but much better than the lens used without the diaphragm.

Around that center hole were a series of smaller holes that allowed light to pass through the periphery of the lens. Light from the periphery would be out-of-focus relative to the light from the center, so there was an in-focus image with an out-of-focus image overlaying it. (The size of the smaller openings was controllable, so you could adjust the degree of softness.) The Canon 135/2.8 SF lens uses a different method to achieve a similar effect, but it's the spherical aberration (the fact that the lens can be simultaneously in and out of focus) that does the trick. That means that simply blurring the image won't work -- at the very least, it needs to be a combination of a sharp image and one that's been blurred somewhat. More than one blurred image with different amounts/types of blur can work better.

Beyond that, you need to keep in mind that shadows (no light) from the out-of-focus part of the image can't contribute anything to the image. In the end, a classic soft focus image will be characterized by an overall loss of detail in bright areas, and a sort of etherial "halo" that bleeds from the highlight areas into the shadows. You can approximate that with a blending mode that only lighten the underlying sharp image, and that has a blend range that ignores the darkest tones in the blurred image (and preferably one that can graduate this cut-off).

Most of the higher-end image editors I've used can do this (with a greater or lesser degree of difficulty). Frankly, it's a heck of a lot easier to use a plugin. I know that Topaz Labs has a couple of plugins that will do it, and I'm pretty sure that NIK Color Efex can do it as well. No doubt Alien Skin and others can supply a plugin for Photoshop that will do the trick, and there are a number of plugins for the GIMP that do classic soft focus effects (I haven't evaluated any of them, so I can't recommend one to you).

@Stan Rogers - While your answer provides some nice history into the optics of soft focus, its only your last paragraph that actually answers my question and it just barely touches on it at that.
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rfuscaJun 18 '11 at 4:02

+1 - Topaz and Nik both have plugins to do it.
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John Cavan♦Jun 18 '11 at 4:04

3

@rfusca - knowing what a soft focus image is is a necessary starting point for recreating it. The third and fourth paras each contains an element of the procedure (not directed at any particular editor) and the they (and the proceding two) explain why it's necessary. The last para is simply "buy a plugin", which is the least useful from a roll-it-yourself point of view.
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user2719Jun 18 '11 at 4:11

1

I actually find this answer to be excellent, and directly describes "How to approximate soft focus digitally". Stan does give a possible recipe for doing that in software.
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ysapJun 30 '11 at 16:31

yeah this actually a pretty good method that, whilst simple, gets you pretty close to the look of a classic soft focus lens (and the results of a more sophisiticated soft focus plugin too!
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Matt GrumJun 18 '11 at 9:00

After reading Stan Rogers' answer, this seems to be the 1st order approximation and a step in the correct direction. Obviously, selective blending will make it more accurate.
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ysapJun 30 '11 at 16:33

I implemented an attempt to simulate it in the way Matt suggested (method 3): blur with a certain window size, blend it with a alpha depending on the brightness (of the blurred layer, not the original) - though not linearly, but "gamma adjusted" by an "effect amount" setting, and applying it only when the result is brighter (Max(I1,I2)).

In the current form it "underdoes it", but note also that the brightness is not true due to clipping, so the white and bright greens are actually brighter and should account for more blur, as you see on the comparison below: (Left: normal lens. Middle: simulation Right: softfocus lens. From wikipedia http://en.wikipedia.org/wiki/Soft_focus )

Does it just simulate blur from focus / depth of field, or does it do soft focus as well?
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mattdmJan 9 '13 at 20:38

Mostly depth of field, but if you dial it in right, it can provide a smoother effect. I interpreted the question as 'how to I achieve a convincing shallow depth of field digitally', rather than 'how to I emulate the effect of a soft focus lens'. So I suppose my answer could be more or less helpful based on the original poster's intention.
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cadmiumJan 9 '13 at 21:03